1. Field of the Invention
The invention relates to an apparatus, constructed for operation in an on-ear mode which apparatus comprises a housing having a housing wall to be applied to an auricle of an ear of a user of the apparatus and which accommodates inside the housing and adjacent the housing wall, an electroacoustic transducer having a diaphragm for producing with its frontside useful sound waves which propagate towards the housing wall and for producing with its rearside, sound waves which are in phase opposition to the useful sound waves, and the housing wall having at least one passage facing the frontside of the diaphragm and through which the useful sound waves can reach the auricle of an ear, and at least one additional passage, which is laterally offset with respect to the frontside of the diaphragm and through which the sound waves of opposite phase can reach the auricle of an ear.
2. Description of the Related Art
Such an apparatus of the type defined in the opening paragraph is commercially available as a portable telephone and includes an electroacoustic transducer manufactured by the Philips Electronics. In the known apparatus, the transducer housing of the transducer is directly secured to the housing wall which is to be applied to the auricle of an ear of a user of the known apparatus, the housing wall having several passages, in the form of holes of comparatively large diameter, and a chamber enclosing a given air volume connected to the transducer at its side which is remote from the housing wall, this chamber being small through-holes in a bounding wall which faces the housing wall of the housing of the known apparatus, these holes providing acoustic friction and via which acoustically damped sound waves of opposite phase are passed through a number of through-holes which each form an additional passage. In the known apparatus, a comparatively intricate construction is used and the known apparatus is constructed only for operation in an on-ear mode. Obviously, the known apparatus can also perform an acoustic reproduction while it is off a user's ear, but due to the specific construction, the reproducing conditions are acoustically unacceptable because in particular, the reproduction volume is inadequate and also because the sound pressure frequency response obtained while the apparatus is off the ear is not satisfactory.